The demographic Transition Model and Variations within it in the steps to an industrialised economy.

The decline in population growth rate is due to the demographic transition from high birth and death rates to low birth and death rates as a country develops from a pre-industrial to an industrialized economic system. This is typically demonstrated through the demographic transition model developed in 1929 by Warren Thompson which is based on an interpretation of demographic history over the previous 200 years in industrialising societies . Thompson identified 4 stages:

Death rates and birth rates (number of people per 1000 population per year) are high and roughly in balance in an agrarian and pre-industrial society, with growth rates less than 0.05%. Population growth is typically very slow in this stage, because the society is constrained by the available food supply

Death rates drop rapidly as a country develops its economy, technology and education, to improve its food supply (selective breeding and crop rotation) and sanitation (food handling, water supply, sewage, and personal hygiene). Access to technology, education in basic healthcare, and increases in female literacy reduce mortality too, especially childhood mortality. Without a corresponding fall in birth rates (and fertility) there is an imbalance and countries in this stage experience a large increase in the rate of population growth (percent growth over a period divided by number of years).

A fall in birth rates and fertility rates (number of children per woman) due to increases in wages, more urbanization, less subsistence agriculture, the improved status and education of women, access to contraception, more parental investment in the education of children as children’s work becomes less valued. Population growth begins to slow down.

4.Birth and death rates are relatively lowand more in balance, with some variations. Birth rates can drop to well below replacement level leading to a shrinking population, a threat to industries that rely on population growth. Death rates may remain consistently low or increase slightly due to more lifestyle diseases from unhealthy diets, little exercise and high obesity. As the large group born during stage two gets older, it creates an economic burden on the shrinking working population. The ratio of working age people to older people is likely to decline substantially in all countries, even those that currently have young populations.

As with all models, this is a generalised picture of population change and may not accurately describe particular countries. Most developed countries are in stage 3 or 4 of the model; the majority of developing countries have reached stage 2 or stage 3. The major (relative) exceptions are some poor countries, mainly in sub-Saharan Africa and some Middle Eastern countries, which are poor or affected by government policy or civil war, notably Pakistan, Palestinian territories, Yemen, and Afghanistan – and, as in Africa, epidemics such as AIDS or Ebola. China, Brazil, Thailand and others have passed through the stages very quickly due to fast social and economic change. China also had programmes to emphasise the quality rather than quality of children from 1972 followed by the one child family planning law from 1980 which brought the fertility rate down to 1.2 or 1.5 children per woman until the two child policy in 2015. There are variations in the developed economies too. In some, such as Japan and some European countries, there is negative population growth (i.e. a net decrease in population over time), mainly due to low fertility rates. In the UK a 15% growth rate (.6% versus 3% in many EU countries) has been predicted between 2014 and 2039, mostly due to net immigration and the birth rates in migrant families.

For the world as a whole the 2015 estimates of birth rate (births per 1000) was 18.6, and the death rate 7.8 (deaths per 1000) See the World Fact Book